The present invention relates to a travel motor hydraulic control system for a construction machine such as a hydraulic excavator and the like.
A travel motor hydraulic control system for construction machine such as a hydraulic excavator and the like have provided in the prior art, a respective hydraulic motor positioned at each side of the machine which is respectively supplied with the pressurized fluid, so as to rotate the respective wheel through the directional control valve from a hydraulic pump. In this type of the travel motor hydraulic control system, a left and right hand motor are designed to be supplied with the combined pressurized fluid of the hydraulic pumps through the directional control valve so as to ensure straight travel of the machine.
Variation in the flow of the pressurized fluid from respective hydraulic pump tends to prevent the machine from traveling straight when it is in a straight run. Under these circumstances, in the construction machine having a travel motor hydraulic control system for the hydraulic motor, a connection line is provided to connect the left hand hydraulic motor drive circuit disposed between the hydraulic motor and the associated directional control valve with the right hand hydraulic motor drive circuit disposed between the right hand hydraulic motor and the associated directional control valve, thereby enabling one motor drive circuits to communicate with the other motor drive circuit, when it is running such that the machine can travel straight and to prevent the machine from performing zigzag travel due to the occurrence of differential flow of the hydraulic pumps
There are known means for ensuring straight travel in construction machine such as a hydraulic excavator. For example, Japanese unexamined patent publication 1997-32043 published on Feb. 4, 1997 assigned to Shin Caterpillar Mitsubishi, Japanese unexamined patent publication 1997-37248 published Feb. 10, 1999, assigned to the assignee of the present application, and Japanese unexamined patent publication 1999-131530 published on May 18, 1999 to Hitachi Construction Machinery are disclosed.
The Japanese unexamined patent publication 1997-32043 discloses a travel control system where a shut-off valve disposed in the control circuit is operated such that the respective hydraulic pump can individually drive the associated hydraulic motor for ensuring straight travel with the machine carrying out operation. The shut-off valve is changed to move in the valve-opening position, so that one of the hydraulic pumps can solely drive the hydraulic motors to keep the machine driving. Furthermore, Japanese unexamined patent publication 1997-37248 discloses a travel control system where a pressure compensating valve that is disposed between a hydraulic motor and a outlet port of associated directional control valve, through which a delivery fluid from a hydraulic pump is supplied to an associated hydraulic motor, connects either of the motor drive circuits to the other motor drive circuit when the pressure compensating valve acts with the pressure at an inlet port thereof, and ensures straight travel.
Further, Japanese unexamined patent publication 1999-131906 discloses that the hydraulic pump individually drives an associated hydraulic motor when the machine is merely traveling, and a shut-off valve is disposed in a connection line between both travel motor drive circuits and is operative to interrupt the connection between the motor drive circuits when the machine is performing a work operation during traveling. As a result, the machine provides a straight travel. Further, Japanese unexamined patent publication 2000-73409 discloses a travel motor drive circuit where a pressure compensated divider is individually disposed between a left and right hand hydraulic pumps and a left and right hand hydraulic motor drive circuit along with attachment drive control circuit, and equally supplies the pressurized fluid to the both motors when the machine is performing a work operation during traveling. As a result, the vehicle provides straight travel.
Thus, many applications have long provided for improving the technology relative to straight travel of the construction machine driven by the hydraulic motor such as a hydraulic excavator. However, those applications have intended merely to maintain a crawler type construction machine traveling straight, when performing works during traveling on a relatively flat ground. In case that the construction machine travels up on the slope with either side track subjected to slip, the pressurized fluid from the hydraulic pump flows only to the light loaded motor which is driving the sprocket under slip and starts to abruptly rotate the motor and the associated sprocket. On the other hand, since the opposite side motor is supplied with a small amount of pressurized fluid, the pressure for driving the opposite side motor is reducing causing the wheel to stop rotating. This results in a downhill steer occurs on the side of the sprocket under slip, resulting in the vehicle preventing from traveling straight. This kind of the problem may occur where either side of the track is subjected to a heavy load while the vehicle is traveling in a mud. The methods have long been required to provide for preventing the vehicle from traveling zigzag under the load variation while it is traveling up a slope. However, the aforementioned drawbacks have not been overcome.
The present invention is directed to overcoming the foregoing and other shortcomings and drawbacks of travel control of a construction machine. The object of the present invention is to provide travel control that a controller mounted on the machine that receives a differential electrical signal representative of the differential pressure from the travel pressure control valve connected to manually operable control levers when machine is traveling, determines if the differential electrical signal exceeds a predetermined value, the machine is steered in the reverse direction of the wheel under slip. It is assumed the machine is traveling straight if the differential electrical signal is less than respective predetermined value. With such circumstances, in the case where the load pressure is less than a predetermined value while the machine is running on the flat ground, the machine is recognized to travel up a slope if the load pressure exceeds a predetermined value.
In order to achieve the foregoing object, the machine in the present invention provides a travel control system for a construction machine having a left and right hand hydraulic pump which supply individually pressurized fluid for a left and right hand travel motor, and the associated directional control valve comprises:
a pilot operated shut-off valve disposed in a connection line which communicates to the left and right hand travel motor drive circuit,
a controller containing a first storage unit storing a determination function of traveling straight and the second storage unit storing a determination function of traveling up a slope, receives a control signal representative of a travel control lever stroke sensed by a position sensor and a control signal representative of pressure in respective travel motor circuit sensed by the pressure sensor, determines whether the machine is traveling straight on a flat ground or traveling up a slope, and transmits a command signal to a solenoid operated valve to move the pilot operated shut-off valve towards the valve-closing position, which results in the travel hydraulic motors individually being supplied the pressurized fluid from the hydraulic pumps.
According to the embodiment of the present invention, the respective travel hydraulic motors are normally supplied with the pressurized fluid from the hydraulic pump through the shut-off valve disposed in the connection line which communicates to the both travel motor drive circuits. In the case where the machine travels up a slope, the differential pilot pressure or the differential potential through actuation the left and right hand operation device or electric levers is respectively generated and either load pressures is created, the controller determines whether the differential pilot pressure or the differential potential and the load pressures exceed respectively a predetermined value or not. If the differential pilot pressure or the differential potential is below a predetermined value and the load pressure exceeds a predetermined value, the controller transmits a command signal to the solenoid operated valve to move the pilot operated shut-off valve toward the valve-closing position.
Consequently, both the hydraulic pumps are supplied independently with the pressurized fluid to the corresponding hydraulic motors, and thereby compelled to independently provide straight travel. Even if a slip is created on either of track when the machine is traveling up a slope, the machine is controlled to ensure for providing a straight travel without stopping the machine and engaging downhill steering due to a slip.
According to another embodiment of the present invention, the controller is desirably controlled to transmit the control signal, which is to fed through the solenoid operated valve from a fixed displacement type hydraulic pump, to the shut-off valve if the differential pilot pressure of the travel directional control valves which are connected to the travel motor operable devices, exceed a predetermined value. In case that a electric lever is replaced for the travel motor operable devices, the controller is desirably controlled to transmit a control command signal, which is fed through the solenoid operated valve from the fixed displacement type hydraulic pump, to a shut-off valve if a differential potential through actuation the electric lever exceed a predetermined value.
With such construction, if the differential pressure generated at the travel control valves connected to the travel motor operable devices or the differential potential reaches the predetermined value and the travel load pressure exceeds the predetermined value during traveling, the controller transmits a operation signal to move the shut-off valve towards the valve-closing position to a pilot portion thereof. Consequently, both the hydraulic pumps individually supplied with the pressurized fluid to exert a load pressure to the hydraulic motors. Thus, the present invention has the advantage that even if a slip is created on either of track when the machine is traveling up a slope, a recovery force is obtained to provide straight travel without stopping and exerting downhill steering on the sprocket under slip. As result in the machine is able to travel straight.
Further, if the differential pressure generated at the travel control valves or the differential potential through actuation of the electric lever exceeds the predetermined value, the controller recognizes that the machine is performing a steering operation. Still further, when the differential pressure generated at the travel control valves or the differential potential through actuation of the electric lever exceeds the predetermined value, the controller determines that the machine is traveling up a slope if the load pressure is equal to or exceeds a predetermined value, on the other hand, the machine is running on the flat ground if the load pressure is less than a predetermined value.
Additionally, an inclinometer, or a detecting means for measuring a tilt angle of the machine, is desirably mounted on the machine to generate a signal representative of the inclined angle of the machine to direct to the controller. The controller determines whether the machine is traveling up a slope or not, based on the signal detected by the inclinometer as well as based on the load pressure in the travel control circuit.